Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Cash and cash equivalents:
Cash and due from banks	$ 457,130	$ 229,901	$ 361,816
Interest-bearing deposits with banks	7,696	7,456	4,690
Federal funds sold and securities purchased under agreements to resell	165,908	180,512	246,109
Total cash and cash equivalents	630,734	417,869	612,615
Investment securities:
Securities held to maturity (fair value of $10,232, $10,233, and $11,427, respectively)	9,659	9,659	10,891
Securities available for sale, at fair value	808,396	806,766	793,124
Other investments	9,031	10,518	10,518
Total investment securities	827,086	826,943	814,533
Loans held for sale	87,342	61,934	57,609
Loans:
Loans, net	5,666,720	5,680,688	5,571,253
FDIC receivable for loss share agreements	16,713	22,161	60,484
Other real estate owned (covered of $12,026, $16,227, and $29,003, respectively; non-covered of $24,070, $26,499, and $35,144, respectively)	36,096	42,726	64,147
Premises and equipment, net	171,565	171,772	187,127
Bank owned life insurance	99,751	99,140	97,314
Deferred tax assets	40,629	42,692	67,997
Mortgage servicing rights	21,510	21,601	20,925
Core deposit and other intangibles	47,223	49,239	57,568
Goodwill	317,688	317,688	317,688
Other assets	58,525	71,774	61,715
Total assets	8,021,582	7,826,227	7,990,975
Deposits:
Noninterest-bearing	1,757,302	1,639,953	1,585,055
Interest-bearing	4,876,355	4,821,092	5,049,496
Total deposits	6,633,657	6,461,045	6,634,551
Federal funds purchased and securities sold under agreements to repurchase	276,774	221,541	254,985
Other borrowings	55,003	101,210	100,963
Other liabilities	48,584	57,511	66,313
Total liabilities	7,014,018	6,841,307	7,056,812
Shareholders' equity:
Preferred stock-$.01 par value; authorized 10,000,000 shares; no shares issued and outstanding
Common stock - $2.50 par value; authorized 40,000,000 shares; 24,156,759, 24,150,702, and 24,118,243 shares issued and outstanding, respectively	60,392	60,377	60,296
Surplus	702,648	701,764	698,079
Retained earnings	241,526	223,156	179,842
Accumulated other comprehensive income (loss)	2,998	(377)	(4,054)
Total shareholders' equity	1,007,564	984,920	934,163
Total liabilities and shareholders' equity	8,021,582	7,826,227	7,990,975
Non-acquired loans
Loans:
Loans, gross	3,586,405	3,467,826	2,979,958
Less allowance for non-acquired loan losses	(33,538)	(34,539)	(34,669)
Credit impaired | Acquired loans
Loans:
Loans, gross	866,504	919,402	1,113,763
Non-Credit impaired | Acquired loans
Loans:
Loans, gross	$ 1,247,349	$ 1,327,999	$ 1,512,201